Internal combustion engines combust a fuel and air mixture within cylinders driving pistons to produce drive torque. The engine drives a transmission through a coupling device. The engine also drives other loads including, but not limited to, an alternator, a plurality of pumps (e.g., oil and coolant) and an A/C compressor. The engine is operated based on a desired air-to-fuel (A/F) ratio. In some instances, the A/F ratio is lean (i.e., reduced fuel) and in other instances, the A/F ratio is rich (i.e., increased fuel). An ignition system initiates combustion of the A/F mixture within cylinders.
During vehicle operation, periods of engine idle occur. Engine idle occurs when the vehicle is at or near zero speed and there is no operator throttle input (i.e., operator not revving the engine). During engine idle, rough idle can occur, whereby the engine speed bounces or drops below a threshold level, resulting in engine stall. Rough idle detracts from vehicle quality and customer satisfaction.
In traditional vehicle systems, low idle and high idle diagnostics have been implemented. These idle diagnostics, however, only check the length of time at which an engine idle speed is above or below high and low idle speed thresholds, respectively, and fail to identify the root cause of the rough idle condition.